Description of Change

This is part of a series to update the lifecycle of NativeWindow::widget_ to use non-deprecated views API, e.g. using views::Widget::MakeCloseSynchronous().

There's a lot of work to do first though. For example, we have a lot of code that calls window->widget()->foo() and it's nontrivial to figure out which code paths will be reachable when widget() is nullptr after we make its destruction synchronous. So I'm going to remove some of the footguns by reducing public use of NativeWindow::widget().

This PR moves the implementation of api::BaseWindow::SetTitleBarOverlay() into a new method NativeWindowViews::SetTitleBarOverlay(). The main motivation to reduce public use of NativeWindow::widget(); but since code being moved fits better in NativeWindowViews, it improves data hiding in several ways:

• api::BaseWindow no longer needs to call NativeWindow::widget()
• NativeWindowViews::set_overlay_button_color() can be made private
• NativeWindowVeiws::set_overlay_symbol_color() can be made private
• NativeWindow::set_titlebar_overlay_height() can be made protected
• Improved demeter. BaseWindow no longer needs to know about Widget internals, e.g. it no longer calls NativeWindow::widget()->non_client_view()->frame_view() and no longer needs to know what derived type it should use when downcasting that NonClientFrameView*.

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: none.